The present invention relates to apparatus for transmitting reciprocatory motion by resorting to rotary feed screws and nuts whose internal threads mate with the external threads of the feed screws. More particularly, the invention relates to improvements in apparatus which can be utilized with advantage in machine tools of various kinds to reciprocate one or more mobile components, e.g., to reciprocate the work-supporting table of a surface grinding machine.
It is well known to provide the underside of a work-supporting table with a nut (or to machine the nut directly into the table) and to bring the internal threads of the nut into mesh with the external threads of a feed screw which is mounted for rotation about a fixed axis and is driven by a reversible electric motor to move the table back and forth, depending on the selected direction of rotation of the motor. Such mode of reciprocating the table is acceptable when the speed of the table is low and when the workpiece or workpieces on the table need not be treated with a very high degree of accuracy. However, the situation is quite different in modern high-speed machine tools, such as precision surface grinding machines, which must be capable of treating the workpieces with a very high degree of accuracy and in such a way that the ultimate finish of each of a short, medium long or very long series of workpieces is always the same. The requirements regarding the accuracy apply not only to the dimensions of the workpieces but also as concerns the finish of their surfaces.